Study of Ferrites Using X-Ray Photoelectron Spectroscopy

Abstract

X-ray photoelectron spectroscopy (XPS) in ferrites (MFe2O4; M is divalent transition metal (TM) ion) materials is capable to differentiate between chemical states with the help of intensive investigation of Fe 2p, and M 2p spectra, particularly through splitting into their components, detecting chemical shifts, and shake-up satellites. Therefore, it could shed light on the behavior of Fe2+/Fe3+, M2+/M3+, and even partially filled site occupancies. The binding energy of ions is influenced by several factors, such as average ligand electronegativity, metal-to-charge transfer, initial state effect, screening effect and relaxation effect that elucidate the role of the surrounding of ions to be probed. Hence, identification of cations in different surroundings is another feature of XPS. Thus, detailed deconvolution of Fe and other metal core-level spectra of ferrites can provide insights into the cation inversion, an important factor that directly governs the performance of ferrite-based devices in spintronics, catalysis, and energy storage. Hence, XPS is not just an analytical tool that can bring the oxidation states into consideration, but a quantitative probe that can clarify cation-inversion profiles and site occupancy. Thus, this review article summarizes the extensive XPS studies on ferrites, focusing mainly on spinel ferrite systems and doped ferrites.